For the past 14 years we have preserved dog kidneys for 1 to 7 days and then tested them by reimplanting them into the same dog. Two years ago continuous perfusion at 8-10 degrees C with a plasma protein fraction for 7 days was followed by successful reimplantation even after immediate contralateral nephrectomy in 3 out of 5 attempts. However, a second batch preserved only 1 out of 6 kidneys successfully and a third batch, 0 out of 5 for 7 days (but 3 out of 3 for 3 days.) A fourth batch preserved 3 out of 4 for 4 days but none for 7 days. Sacks' solution has been used for flush of kidneys followed by simple cold storage. It preserved 1 kidney successfully for 2 days, and 1 for 3 days. For 4 day storage 2 attempts out of 13 were successful. The renovascular response of hypothermic rabbit kidneys to adrenergic drugs at 3 degrees C has been investigated in vitro. The study will be repeated with dog kidneys. The influence of DMSO (dimethyl sulfoxide) concentration and of cooling rate on ice crystal loci in frozen hearts and kidneys has been studied with electron microscopy. The toxicity of very high DMSO concentrations in the perfused kidney at subzero temperatures will be studied by physiological and electron microscopic techniques. Attempts will be made to cool a kidney to -79 degrees without freezing.